This invention relates to test stands including dynamometers for testing rotary outputs of mechanisms as, for example, vehicles.
Manufacturers of quality mechanical power sources almost invariably test the source prior to releasing the same for sale to ensure that the source is performing properly and is up to its rated capability. In some cases, the testing has been performed with dynamometers, while in others, the testing has been performed by other means.
Dynamometer testing is generally preferred over other forms of testing by reason of an increased reliability of test results due to the elimination of subjective judgment on the part of operators and/or observers through the use of measuring apparatus. However, dynamometer testing is not altogether satisfactory, particularly where the mechanical power source being tested is operated at a relatively low speed and/or has a high torque output. For example, in crawler type vehicles, where the testing is to be performed at the final drive, rotational speeds of 100 rpm or less and high torque outputs are invariably present. Conventional dynamometers cannot adequately measure desired operational parameters in such cases or, if capable, are extremely costly, thereby discouraging their use. Consequently, the testing of power sources, such as crawler type vehicles, has generally been performed on a test track under the control of an operator with the result that the test results may be unreliable due to subjectivity involved on the part of the operator during the testing procedure.
To overcome the foregoing difficulty, Bartlett et al in the commonly assigned U.S. patent application Ser. No. 763,315, filed Jan. 28, 1977, Pat. No. 4,063,234, entitled "Testing Apparatus" and Kinney, in the commonly assigned U.S. patent application Ser. No. 763,316, filed Jan. 28, 1977, Pat. No. 4,092,855, entitled "Dynamometer and Coupling for a Test Stand", have proposed testing apparatus and test stand constructions based on a dynamometer utilizing a liquid cooled, automotive disc brake to drastically reduce the cost of dynamometer testing such vehicles. The constructions proposed have worked extremely well and reliably for their intended purpose. They are, however, somewhat complex in construction, requiring large, precision bearings for rotatably supporting the dynamometer housing and expensive couplings for coupling the dynamometer to a chuck which engages the vehicle rotational output, which couplings are required to compensate for misalignment between the rotational output of the vehicle to be tested and the rotational axis of the dynamometer.